Metal bioavailability in freshwater sediment samples and their influence on ecological status of river basins

The general aim of this work has been to check the ecological impact of metals on the Ebro river basin. In order to evaluate this, metal behavior considering water, sediment as well as metal bioaccumulation in fish has been studied. Total concentrations of metals, as well as the potentially bioavailable fraction of metals in sediment has also been analyzed by the application of the sequential extraction method (BCR method). In order to evaluate the influence of metal pollution on the river ecological status, according to the Water Framework Directive (WFD), diverse biological indices such as macroinvertebrates (IBMWP), diatoms (IPS) and macrophytes (IVAM), have been considered from an integrated point of view. Considering both water and sediment, metals which contributed in higher extend to the reduction of biological quality have been demonstrated to be Pb and Zn, as they presented a negative influence on macroinvertebrates, diatoms and macrophytes communities. As and Cr that seemed to have a significant influence on macroinvertebrates and diatoms too, while Ni negatively influenced only diatom communities. This study also demonstrated that monitoring programs only based on total metal determination in water are inefficient, as metals present even at undetectable concentrations in water are strongly accumulated in fish. Moreover, the high concentrations of Hg found in sediments indicated that this river basin may present pollution problems regarded to this metal, as demonstrated by the high Hg levels found in fish.